1. Field of the Invention
The present invention relates to an antenna apparatus for transmitting or receiving radio waves in two or more frequency bands, and in particular, to an antenna apparatus capable of being installed in a portable wireless communication apparatus such as a portable telephone.
2. Description of the Related Art
Recently, portable telephones are rapidly proliferating, and a demand for use with a broader frequency band is increasing so as to improve transmission efficiency and prevent a noise as well as interference in the portable telephone. Because an antenna construction of a conventional portable telephone does not allow to be used with a wide frequency band, developments of new antenna apparatus and methods, which are operable at a plurality of frequencies, and able to realize a broader band wireless transmission and reception, are in progress.
FIGS. 1 and 2 show examples of antennae which are operable in a plurality of frequency bands. FIG. 1 shows such an example using a parasitic antenna element, and FIG. 2 shows such an example using a plurality of radiating conductors.
In an antenna 180 shown in FIG. 1, a coaxial line 181 is connected to a dielectric substrate 182. In this dielectric substrate 182, a radiating conductor element 183 and a parasitic element 184 are disposed in proximity. This arrangement is widely used for obtaining a multiple resonant characteristic. Further, in an antenna 190 shown in FIG. 2, where no parasitic antenna element 184 is used, a plurality of radiating conductor elements 192 and 193 each having a different resonance frequency is arrayed on a substrate 191, and they are supplied with power from single feed point 194 to obtain a multiple resonant characteristic. By way of example, the antenna 190 is grounded at a ground point 195.
The antenna 180 having the parasitic antenna element disposed therein as shown in FIG. 1 involves such a problem that a discretionary arrangement of antenna elements is impossible because that a relationship in positions between the parasitic antenna element 194 and the radiating element 193 has a significant influence on a characteristic impedance of its antenna apparatus.
Also, in the antenna 190 shown in FIG. 2, in which no parasitic antenna element is disposed, there is required a large space for accommodating the radiating elements 192 and 193 arrayed therein which resonate in a plurality of frequency bands. In addition, this type of antenna has such a problem that the antenna may not be operable if these frequency bands are in proximity and overlap by approximately 10%. This is because that in such an arrangement as of the antenna 190, a multiple resonant of respective radiating conductors 192 and 193 is realized by spacing apart therebetween by means of a slit and operating them at respective resonant frequencies. However, because of a certain degree of broad band characteristic owned by respective radiating conductors 192 and 193, if their frequency bands are in close proximity, the effect by the slit to space apart therebetween and the multiple resonant are not attained. Despite of the above, it is required to be operable at frequencies which are in proximity for use in the aforementioned portable telephone.